554 PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



every instance of motion being in this way produced, it was in truth owing to 

 some part of one of the metals having been abraded by the other; so that, 

 under the appearance of 1 metal, 2 were in reality applied. But it can scarcely 

 be supposed, that from touching the polished surface of tin-foil in the gentlest 

 manner with the smooth round end of a silver probe, any part of the former 

 metal was carried away by the latter; and even when friction was used, as the 

 zinc was much harder than the gold and silver, it is not probable that it was 

 in the least abraded by them. Besides, moisture, as I have already said, in- 

 creases this effect of friction, though it lessens friction itself. 



The most powerful argument however, in favour of my opinion, is another 

 fact I discovered in pursuing this subject; which is, that an exciting power may 

 be given to a metal by rubbing it on many substances besides another metal, 

 such as silk, woollen, leather, fish-skin, the palm of the human hand, sealing, 

 wax, marble, and wood. Other substances will doubtless be hereafter added to 

 this list. 



As the metals, while they were rubbed, were held in my hand, which, from 

 the dryness of its scarf-skin, might have afforded some resistance to the passage 

 of small quantities of the electric fluid; and as the substances on which the 

 friction was made, were either electrics, or imperfect conductors of electricity; 

 I once thought it possible, that the metal subjected to the friction had acquired 

 by means of it an electrical charge, which, though very slight, was still sufficient 

 to act as a stimulus on the nerves to which it was communicated. But that this 

 was not the case was afterwards made evident, by the following experiments and 

 considerations. 



1. A metal, rendered capable by friction of exciting contractions, produced 

 no change on Mr. Bennet's gold-leaf electrometer. 2. The interposition of 

 moisture does not, in any instance I know of, increase the effect of friction in 

 exciting the electric fluid. In some instances it certainly lessens this eflect. 

 But moistened substances, when rubbed by a metal, communicate to it the ca- 

 pacity of producing contractions, much more readily than the same substances 

 do when dry. 3. If my hand, from being an imperfect conductor, had occa- 

 sioned an accumulation of electricity in the metal which was rubbed, a greater 

 effect of the same kind ought certainly to have been produced by insulating the 

 metal completely; which is contrary to fiict. 



4. I placed a limb of a frog, properly prepared, on the floor of my chamber; 

 if a severe frost had not prevailed when I made this experiment, I should have 

 laid it on the moistened surface of the earth. I then raised from the muscles, 

 by means of an electric, the loose end of the nerve, and touched it with the 

 rubbed part of a piece of metal; but no contractions followed. To be convinced 



